It is common for a work machine to have multiple functions with each function having at least one actuator. For example, a wheel loader has a lift function and a tilt function. Commonly, in such machines, a prime mover drives a hydraulic pump for providing fluid to the actuators. Open-center valves control the flow of fluid to the actuators.
Some modern machines have replaced the traditional hydraulic system described above with an electro-hydraulic actuators (“EHA”) system. An EHA includes a reversible, variable speed electric motor that is connected to a hydraulic pump, generally fixed displacement, for providing fluid to an actuator for controlling motion of the actuator. The speed and direction of the electric motor controls the flow of fluid to the actuator. Power for the electric motor is received from a generator, a power storage unit, such as a battery, or both. A system that includes an EHA is referred to herein as an electro-hydraulic actuator (EHA) system.